How to Show Account-Related Cases on the Opportunity Page Layout in Salesforce

In Salesforce Classic

1. Navigate to Setup | Customize | Opportunities | Page Layouts
2. Click Edit next to the page layout name.
3. Select Related Lists from the left-hand pane of the palette.
4. Drag and drop Cases to the Related Lists section of the layout.
5. Click Save.

In Lightning Experience

1. Navigate to Setup | Object Manager | Opportunity | Page Layouts
2. Click Edit from the dropdown arrow on the right.
3. Select Related Lists from the left-hand pane on the palette.
4. Drag and drop Cases to the Related List section of the layout.
5. Click Save.

You can now view all Cases related to an Account when viewing an Opportunity associated with that Account.

It’s recommended that you add the Opportunity Name to the Cases related list, so that the user knows which Cases are related to the Opportunity in question.